1. Field of the Invention
The present invention relates to a valve open-close indicating apparatus for indicating an open or closed state of a valve, such as a gate valve, butterfly valve, etc.
2. Description of the Related Art
In a valve, such as a gate valve or butterfly valve, a piston is reciprocated by means of pneumatic pressure, hydraulic pressure, etc., and a valve plug is reciprocated with respect to a valve seat, whereby the valve is opened and closed.
The valve of this type is provided with an open-close indicating apparatus for indicating the current state of the valve, open or closed. Thus, an operator can confirm the open or closed state of the valve, and therefore, can be prevented from wrongly operating the valve. To attain this, the open or closed state of the valve must be indicated correctly, so that the indicating apparatus requires high reliability.
The conventional open-close indicating apparatus is provided with, for example, a limit switch which is turned on and off as the piston reciprocates. In response to this on-off operation, the indicating apparatus indicates "open" or "closed."
On rare occasions, however, the limit switch of the conventional indicating apparatus cannot be shifted following the reciprocation of the piston. In such cases, therefore, the indicating apparatus may undergo wrong operation, so that its reliability is not satisfactory.
Further, maintenance work sometimes requires the valve to be disassembled. Accordingly, the indicating apparatus, as well as the valve, is expected to have a simple structure and be easy to assemble.